1. Field of the Invention
The invention relates to a positive crankcase ventilation system (hereinafter, referred to as “PCV system”) that delivers blow-by gas in an internal combustion engine provided in a vehicle or the like to an intake system. The invention also relates to a cylinder head used for the PCV system, an internal combustion engine including the PCV system, and a positive crankcase ventilation method. Particularly, the invention relates to improvement of a PCV system that includes a blow-by gas collection passage through which an inside of a crankcase is connected to an inside of a breather chamber, and improvement of a positive crankcase ventilation method.
2. Description of the Related Art
In related art, an internal combustion engine for a vehicle includes a PCV system that introduces blow-by gas, which has been blown into a crankcase through a gap between a cylinder and a piston, into an intake system. That is, using the PCV system, the blow-by gas, which contains nitrogen oxide (NOx), carbon monoxide (CO), hydrocarbon (HC), and the like, is delivered to a combustion chamber through the intake system for the engine. This prevents the blow-by gas from being discharged into the atmospheric air. Also, the PCV system introduces new air (outside air) into the crankcase to ventilate the crankcase, thereby suppressing deterioration of engine oil due to the blow-by gas, and maintaining lubricating performance and the like for a long time.
As described in Japanese Patent Application Publication No. 2000-8951 (JP-A-2000-8951), the PCV system includes an oil separator. Oil mist contained in the blow-by gas is separated from the blow-by gas in the oil separator, and the oil is delivered to an oil accumulation portion such as an oil pan. After the oil mist is separated and removed from the blow-by gas, the blow-by gas is returned to the intake system for the engine. As described in the publication No. 2000-8951, for example, the oil separator is disposed in a cylinder head cover of the engine (hereinafter, simply referred to as “head cover”).
For example, Japanese Utility Model Publication No. 7-46724 (JP-UM-A-7-46724), Japanese Patent Application Publication No. 11-223118 (JP-A-11-223118), and Japanese Patent Application Publication No. 2005-133552 (JP-A-2005-133552) describe a configuration where a blow-by gas collection passage, through which an inside of a crankcase is connected to an inside of an oil separator, is provided to increase the level of performance of collecting the blow-by gas from the inside of the crankcase.
In the system that includes the blow-by gas collection passage, for example, an air introduction passage and an oil return passage are provided separately from the blow-by gas collection passage. New air for ventilation is introduced into the crankcase through the air introduction passage. Oil separated from the blow-by gas in the oil separator is delivered downward and collected into an oil pan through the oil return passage.
FIG. 10 is a schematic diagram showing the general configuration of an engine “a” that includes a blow-by gas collection passage “b”, and a manner in which fluids (blow-by gas, new air, and oil) flow in the engine “a”. In FIG. 10, the solid line arrows indicate the flow of the blow-by gas, the dashed line arrows indicate the flow of the new air, and the chain line arrows indicate the flow of the oil.
As shown in FIG. 10, the blow-by gas collection passage “b” is formed to extend in a cylinder block “d” and a cylinder head “e”. An upper end of the blow-by gas collection passage “b” is directly connected to an inside of an oil separator “g” provided in a head cover “f”. That is, the inside of the crankcase “c” is connected to the inside of the oil separator “g” through the blow-by gas collection passage “b”. After the blow-by gas is introduced into the oil separator “g” from the inside of the crankcase “c” through the blow-by gas collection passage “b”, the oil mist is separated and removed from the blow-by gas in the separator “g”. Then, the blow-by gas is introduced into the intake system.
The oil separated and removed from the blow-by gas flows downward into a cam chamber “i” through an oil discharge hole “h” formed in the oil separator “g”. Then, the oil is collected into an oil pan “k” through an oil return passage “j”, using the self weight of the oil. In the system shown in FIG. 10, the oil return passage “j” is used also as an air introduction passage. The new air introduced into the cam chamber “i” flows into the crankcase “c” along with the oil through the oil return passage “j”. Thus, the blow-by gas in the crankcase “c” is diluted with the new air. That is, the blow-by gas diluted with the new air flows toward the oil separator “g” through the blow-by gas collection passage “b”.
In most cases, the blow-by gas collection passage “b” is disposed at a position under the influence of the temperature of outside air, due to limitations of space where the blow-by gas collection passage is disposed. Particularly, in a portion of the blow-by gas collection passage “b”, which is located in the cylinder head “e” disposed above the combustion chamber (i.e., a portion where the temperature is highest), the temperature is relatively low (for example, approximately 5° C. during winter time).
Therefore, when the blow-by gas collected from the inside of the crankcase “c” flows through the portion of the blow-by gas collection passage “b”, which is located in the cylinder head “e”, the blow-by gas is cooled. Accordingly, moisture contained in the blow-by gas may be condensed near an inlet portion of the oil separator “g” (i.e., a portion A in FIG. 10), and inside the oil separator “g”.
In this situation, nitrogen oxide (NOx) in the blow-by gas may be combined with condensation water, and sludge may be generated at the inlet portion of the oil separator “g”, and inside the oil separator “g”. If a large amount of sludge is generated, the oil discharge hole “j” through which the oil separated from the blow-by gas is returned to the cam chamber “i”, and the oil return passage “j” through which the oil is returned to the oil pan “k” may be blocked by the sludge. This may make it impossible to discharge the oil from the oil separator “g” toward the oil pan “k”.
If it is impossible to discharge the oil into the oil pan “k”, a large amount of liquid oil is accumulated in the oil separator “g”, and the liquid oil is delivered into the intake system for the engine along with the blow-by gas. This may decrease the output from the engine, and increase the amount of oil consumption. Also, in the system where the oil return passage “i” is used also as the air introduction passage, it may be difficult to introduce new air into the crankcase “c”.
Further, the generation of sludge may adversely affect a valve operating system of the engine “a”, and interfere with the normal opening/closing operation of an intake valve and an exhaust valve.
As means for suppressing the generation of the sludge, the diameter of the passage through which the new air is introduced into the crankcase “c” may be increased to increase the amount of new air introduced into the crankcase “c”. In this case, it is possible to reduce the concentration of NOx in the crankcase “c” (i.e., dilute the blow-by gas in the crankcase “c”), thereby reducing the concentration of NOx in the fluid (i.e., the mixed gas of the blow-by gas and the new air) flowing through the blow-by gas collection passage “b”.
However, in the configuration where the amount of new air introduced into the crankcase “c” is increased, the flow speed of the fluid in the blow-by gas collection passage “b” is increased. This increases the amount of oil mist that flows from the inside of the crankcase “c” toward the oil separator “g” along with the blow-by gas, that is, the amount of oil mist introduced into the oil separator “g”. In this case, the oil separation function of the oil separator “g” may be insufficient. Accordingly, it may be necessary to replace the oil separator “g” with an oil separator with a larger size, or an oil separator with a higher oil separation function. This increases the cost.
Also, because the amount of new air introduced into the crankcase “c” is increased, the amount of air introduced into the intake system for the engine from the PCV system is increased. In general, the air is introduced into the intake system from the PCV system at a position downstream of an airflow meter (more specifically, downstream of a throttle valve). Also, the amount of fuel injected into the engine is set based on an intake air amount detected by the airflow meter so that an air-fuel ratio is equal to a predetermined air-fuel ratio. Therefore, if the amount of air introduced into the intake system for the engine from the PCV system is increased, the amount of air that is actually introduced into the cylinder is much larger than the intake air amount used for the calculation of the fuel injection amount. As a result, the air-fuel ratio may be higher than the predetermined air-fuel ratio. As a result, a desired engine out may not be obtained, or an engine speed may be unstable during idling operation of the engine (i.e., rough idling may be caused).